FIG. 1 depicts a schematic diagram of wireless network 100 in the prior art, which comprises wireless telecommunication terminal 101 and access points 102-1 through 102-L, interconnected as shown. Wireless terminal 101 uses access points 102-1 through 102-L to exchange blocks of data, or “packets,” with computer servers that are external to wireless network 100. At any given time, wireless terminal 101 is associated with one of access points 102-1 through 102-L for the purpose of communicating with the external servers.
It is important in some operating scenarios to know the location of wireless terminal 101 within wireless network 100. Knowledge of the location of wireless terminal 101 enables services that use end-user location information. Such services include location-aware content delivery, emergency location, services based on the notion of “closest resource,” and location-based access control.
Various techniques for estimating location exist in the prior art.
In accordance with one technique, the location of a wireless terminal is estimated to be at the center of the coverage area served by the access point with which the wireless terminal is associated. This technique is advantageous in that it does not require that additional hardware be added to the wireless terminal or to the wireless network, and this means that the first technique can be inexpensively implemented in legacy systems. The accuracy of the first technique, however, is a function of the size of the coverage area, and, therefore, it is generally not acceptable for applications that require higher accuracy.
In accordance with a second technique, the location of a wireless terminal is estimated by a radio navigation unit, such as a Global Positioning System receiver, that is incorporated into the wireless terminal. This technique is accurate to within a few meters and is advantageous in that it does not require that additional hardware be added to the telecommunication system's infrastructure. The second technique is disadvantageous, however, in that it cannot be used with legacy wireless terminals that do not comprise a radio navigation unit and, furthermore, cannot be used reliably indoors.
In accordance with a third technique, the location of a wireless terminal is estimated by triangulating the angle of arrival or the time of arrival of the signals transmitted by the wireless terminal to be located. Various receivers that are either part of or separate from the access points are part of the triangulation process. This technique is accurate to within a few meters and is advantageous in that it can be used with legacy wireless terminals. It is disadvantageous, however, in that it generally requires that specialized hardware be added to the wireless network, and this is very expensive.
In accordance with a fourth technique, the location of a wireless terminal is estimated by using wireless terminals to make signal measurements and to transmit those measurements to another device for analysis. This technique is accurate to within a few meters and is advantageous in that it exploits a potentially large installed base of wireless terminals. It is disadvantageous, however, in that it cannot be used with some legacy terminals. Such legacy terminals include those that do not have the ability to transmit signal strength measurements and those that do not have the ability to maintain a signal strength measurement database against which to match received signals.
Therefore, the need exists for a technique for estimating the location of a wireless terminal with higher resolution than the first technique and that can be inexpensively implemented in legacy systems.